The fire department said it also rescued Mahoney when he was found unresponsive in the lake. He was transported to a hospital, where he died Tuesday.

Mahoney was a nine-year veteran of the fire department and occasionally was an aide to the chief. He is survived by his wife and three young sons, the department said.

The Dane County medical examiner's office told CNN affiliate WKOW that McCulloch's death "was consistent with an accidental drowning due in part to a medical event." The office continues to investigate Mahoney's cause of death, the fire department said.

"The well-being of our competitors is paramount and we are grateful for the effort and quick support of medical personnel," Ironman said in a statement Sunday to WKOW. "We will continue to work with the local authorities to gather all the details on these incidents and will continue to do everything possible to provide a safe environment for our athletes. In respect of the families and athletes' privacy, we will have no further comment at this time."

"My thoughts are with the families and loved ones of the two athletes who died while competing in the Half Iron Man on Sunday," Rhodes-Conway said. "It is a tragic coincidence that two men died competing in the same event."